Trimable servo tab with balanced, antibalanced, and spring tab action intended especially for aircraft



July 21, 1953 T. N. G. LIDMALM ETAL 2,646,234 TRIMABLE SERVO TAB WITH BALANCEDv ANTIBALANCED, AND v SPRING TAB ACTION INTENDED ESPECIALLY FOR AIRCRAFT.

Filed Dec. 26, 1950 Fig.1

mun/run 1 28a I I Y I 29 21 v 30a 28 19 TORD NILSGOSTA LIDMALMJNVENTORS NILS FOLKE LENNART BENGTSSON.

ATTORNEYJ Patented July 21,1953

part of; the aircraft; 'ment devicef. V

surface. I j I Another object of I a linkage-arrangement in the control surface as above, wherein the linkage arrangement is of simple structure so as-to reduce "links to a minimum;

Svenska {Aeroplad Aktiebolaget; l-Linkoping,

fsweden a joint.-sto clr company ofsweden I 'Apnl cationne'cemh r 26, 95, a I In Sweden January,4,;1 950 v l1 I This inventionrelatjes 'to movable aircraftcom trolsurfaces having tabs hinged thereto, and relates mOreparticuIarly to a-tab actuating-mech- I 'ani'sm' for automatically controlling the'tab ,with

respect to the movablecontrolsurface. I

In high speed and heavy aircraftstheg forc applied bythe pilot for turning the movable con trol surface through larger angles" of displacement are frequently; of such magnitude that it is --ne'ces'sary or desirableto provide .auxiliary meansto assist the-pilotii'n-operating thecontrol surface. forthispurpose there is mountedon the rear edge of the controlsurface a servotab or flap which'isfarranged-to move in a direction opposite to that of -the' control surface, when theconditions are such that the force of 1' air 'streamagainst which the control surface is :to be moved is excessive. To control this'relative movement of the control surface and the servo tab in; response to air loadsjacting uponthe control 'jsurface variousmechanisms havebeen introduced; "In mechanisms of this kinda gearing link'age arrangement; connecting the tab and the control 'surf,ace'with the control surface operatingmeans, is combined-with aspring unit or other yielding connection to provideacombined r V 'f spring" and geared tab. Inaddition, to set the position of the-tab relatively'tolthe control surface such mechanisms I are often combined with a trim adjustment deviceto providea trim tab. Common to these prior mechanisms is that the gearing linkagearrangement is at qleast in part suspended-from and acts'upon astationary fjor' instance the trim adjust- 'Ihe mainobjectof the present invention is to provide in mechanisms of theabove character agearing linkage arrangement of such a structure as to-enable-the linkage to be entirely suspended from and movable together with the movable control I surface whereby' the mounting of. the linkage will be cOnVenient andlight as comparedwith prior linkage arrangements-with a supporting structure outside the movable control the invention is to provide the number of The foregoing and oth'er-objects and advantages will becomeapparent-from the following description of the typical embodiment 'of tl1'e' I invention 'shownin the accompanying drawings Figure 1- is a perspective view-of a; tab actuating- 'm'echanism applied to a rudderofan aircraft and "connected to the rudder control operating means; the rudder being shown with broken lines. Figure z'is'a' cross sectional view taken"submatically shown-in the drawing. I

stannan as indicated by line LIL-11011 rgigure r. Eigure-3 is a 'diag-rammatic view showing the rudder in adeflectedposition and-*thea-tab in diiferent; angular positions relatively to the rud} der. V I I In' the drawings l is a control surface in -the form of-a rudder which is journalledin spaced bea'rings Z and turnable around; anaxis denoted *by the dash dotted line 3. A--tab' 4 is arranged at the trailingedge of the rudder land is mount "ed on hinges 5 insuch a manner as to haveangu lar movement relatively to the rudder I inboth directions from the neutralposition shown-gin Figures 1 and 2- of the drawings. To the' bottom [portion of therudder'l--is;attached a post-'6 the lowerkend i of I 'which' is ri'gidly fi-xed to a 'eb'ra'cket T, having two-radially extending-arms 8; posi'- tioned-one above the other and iormed with axially aligned holes I 9 providing jqurnals for a fixed shaft 10 theaxisof- 'which is coaxial with the rotation axis 3 of the rudder I. A lever l l comprising a pair of diametricallydisposed cable sector parts [2- is-rotatably fixed tothe shaft 10 between the arms 8 and thus rotatablymounted 'relativeto the rudder I. f-Ea'ch -cable sector part 12 is grooved along' its outer curvedperiphery andin" the grooves is laid a cable I3,- which is anchored at the ends to the cable sector parts l2 and runs to theaircraft control compartment Knotshown), wherethe'cable I3 is' connected'to 'the pilotoperated control means; such as pedals l4, and run around guidepulleys I4a as diagram- A two-way acting spring unit -I 5 is arranged-at the side of the bracket I andanchored by-suitable means, such asforks It, at one end to the outer end of an arm I! projecting radially from the bracket 1 and at the other endto the outer portion of one of the cabIeseOtOl'PaIts IZ. As

this spring unit may be of any kind known and does not form a part of our invention per se it will not be described here and shown in detail in the accompanying drawings. It might-be suffioient to pointfout that such a spring unit con- --tains aspring element which tendsto hold the distance between the arm I! and-the cable sector part l2 constant-and is adapted to be compressed or extended axially when theresistance in turning' the rudder l in an anti-clockwise-and clock- I wise direction respectively by means ofthe cable control; system exceeds the initial tension of the spring element. Of course upon remoyal of -such axial forces the spring restores the spring unit V to its normal length and thereby restores the "initial relationship between arm l'l andflsector part 12.

In the rudder l there is mountedyagearing l a a em t in l di e ..cury t ti y's. w ic isl iv ta s n oried t an on a'pin' l9extending parallel with therudderaxis 3 alced relation to the longitudinal centre line A'.-A of the rudder so that the steering arm |B upon movement will swing relatively to the rudder in a plane normal to the axis 3.

the centre line A-A relatively to the 'pin |9.'= One arm of this lever projects outwardly and slightly rearwardly from the pivotpin 2| and is pivotally connected by a pin 22' to one end of a push-pull rod 23, extendingrearwardly to. the I tab 4 and connected thereto by means of a lug 24 and a pivot pin 25, carried by the lug in spaced relation to the rotation axis of the tab as indicated by the dash dotted line 26 in the drawings .;The.other arm of the lever is coupled to a trim adjustment device by means of a pivot means of the :pivot pin '21. The shank 28 engages with a screw threadednut 30 which is rotatably mounted-.on a stationary part of the aircraft,

such as -fork 38a, and carries a pulley 3|. rigidly attached. to. the nutjfi. The nut is adapted to berotated bygcables 32 laid on-the pulley and extending to.the pilots compartment. It will .be seen that upon rotation of .the nut 39 the shankjg ismoved either fore or aft to change or adjust through rod 29 the position of the pivot .21 of thelever 20 and thereby the position of, the tab through lever 20 and rod 43.

Ihe linkage arrangement is adapted to be actuated by; the;; leve,r I through the following connection. nn upright torsion tube 33 is ro- ..tat ably.-mountedat its ends in bearings 34 at tached tostationary parts of the aircraft for rotation about an axis parallel with and spaced irom the rudder axist. The ends of the torsion tube are provided with upper and lower crank arms 35 and 36 respectively, each of which being adapted to receive oneend of a connecting rod ,3? and 3 8 respectiyely, pivotally mounted on the crank 8 1 511 5,inqe s of pivot pins 39 and 40.

The, connectingrods 31 and 38 are of substantially the same length and are disposed one above the otherin planes. normal tothe rudder axis 3 randare attheir other ends pivotally connected respectively to. the free end of the steering arm |8 by means ,of pin 2| and to one of the cable sector parts-. |2 by,a pin-4 disposed substantially right below the pin 2| on the same side of the rudder axis as this pin 2|. As shown in the drawings the; r ods 29 and 3'! are on the same leveland run through a. horizontal slot 42 in the skin of. the f orward part of the rudder while .rod 23 passes through a rear opening 43 in the skin of -.the rudder.

In. operation of the mechanism it will be assumed that the trim adjustment deviceis preset so. thatithe rudder land the tab 4 are in the aligned. neutralpos'ition as illustrated in Figures 1'and?'ofjthe'drawings. It will further be assumed that theupper one of the pedals I4 is actuated by the pilot. A pull is then applied to the upper cable l3 causing an anti-clockwise turning'movement.of the cable segment If the pedal 'isiess than the tension of the A two-armed lever 23 is pivotally mounted on another pin 2|, carriedby theother free. end of the steering arm l8on' oppositesi'de of spring unit I5, which is the case 'movetogethe'r aboutthe rotation axis 3 of the rudder 'Ihe turning movement of the lever l causes a thrust on the connecting rod 38, which moves the connecting rod 38 to the left in the drawings and hence rotates the torsion tube 33 clockwise whereby connecting rod 31 moves the central lever pivot 2| to the left. However, this pivot 2| is also moved to the left by the turning movement of the rudder anti-clockwise about the rotation axis 3. For explanation of the operationoi the mechanism we presume that the leverage ratio is such thatthe movement of the pivot 2| by the lever through connecting rod 38, torsion tube ssand connecting rod 31 is equal to the movement of the pivot 2| in consequence of turning movement of the rudder about axis 3. No relative movement of the pivot 2| with respect to'the rudder I would then occur. If the pivot 21 of the lever 20 Were disp osed coaxially with the axis 3 of the rudderl no deflection of the tab inrelation to'the rudder would be obtained. "However, as previous described the relatively. fixed pivot 2l is positioned on opposite side of the centre line A.A relatively to the pivot 2| and consequently the latter pivot 2| moves forwardly in relation to the rudder when the latter is moved anti-clockwise as supposed. The lever 2c is thereby swung in a clockwise direction and consequently the tab 4 is turned anticlockwise relatively to the rudder. The tab 4 is now operating as a geared tab with anti-servo action as shown by dotted lines in Figure 3.

To make the following operation easier to understand it will be described as occurring step by'step although in'fact the operation proceeds continuously; 1

When by further 'depressing'the pedal I4 the force for turning the rudder against air loads reacting thereupon exceeds the tension of the spring in the-spring unit [5 the rudder movement is discontinued and only the lever continues to move anti-clockwise against the action of the springjwhich is hereby compressed. As the rudder l is stationary during this continuous rotation of the lever I there will be no relative movement of the pivot 2'! andthe rudder In this case the pin 2'! provides a pivot centre for the lever 29 and the pivot 2| is now moved to the left by' the lever, through connecting rod 38, torsion tube 33and connecting rod 31. The lever 20 is thus swung anti-clockwise and consequently the tab 4 is turned clockwise from its anti-servo position towards a reversed position wherein the tab is deflected in opposite direction relatively to the rudder i as shown by full lines in Figure 3. The airstream will now act upon the tab 4 to move the rudder anti-clockwise, i. e. in the direction. desired The'turning of the rudder I has no eiTect upon the lever l as the compressed spring in unit I 5 now extends in the rudder movement direction until the initial relationship between arm I! and sector part I2 is restored. As will -be apparent from the previous description the lever 20 willnow move clockwise relatively to the rudder and the tab 4 will hereby deflect in anti-clockwise direction until the air loads on the rudder again becomes excessive, when the spring is again compressed and the tab deflected in the servo direction. The tab has now operated as a combined geared and spring tab. Of

' 7 course as earlier stated the movement of the tab though this operation of course will be reversed.

From the foregoing description it will be ob-- served that the location of the pivot 21' in relation to the centre line A-A, the rudder axis 3 and the pivot 2| influences the function of the mechanism in the following way:

Pivot 21 is located on the opposite side of centre line A-A relatively to pivot 2| -A geared tab with anti-servo action may be obtained.

The neutral position of the control surface can be trimmed, e. g. during flight, which is effected by the above described trim adjustment device. By pullingone of the other of the cables 32 the nut 30 is rotated, whereby screw shank 30 and rod 29 are axially displaced. As will be seen lever 20 is thereby swung about centre pivot 21 which causes a movement of the push-pull rod 23 and f thus a deflection of the tab 4 to the position wanted.

Having described only one typical form of the inventionwe do not wish to be limited to the specific details set forth but wish to reserve to ourselves any variations of modifications that may appear to those skilled in the art and fall I within the scope of the following claims.

What is claimed is:

1. In an aircraft, a control surface pivotally connected at its forward edge to the aircraftfor movement about a given axis, a tab hinged to the trailing edge of the control surface, a lever, a steering means supported by the control surface and extending in a plane normal to'said given axis, a pivotal connection between the lever and the steering-means, said lever being supported by the steering means for bodily movement of the lever in said plane and turning movement-of the lever in relation to the steering means, a rod means, a pivot connecting one end of the rod means with the lever at an axis spaced from said pivotal connection, a universal joint connecting the other end of the rod means with a fixed part of the aircraft, a push-pull rod operatively conaxis and connected to said control means to be operated thereby, a ore-loaded two-way acting 7 spring unit operating between the control surlever in relation to the steering means, means for trimming the position of the tab relatively to the control surface, a rod means, a pivot connecting one end of the rod means with the lever at an axis spaced from said pivotal connection, a universal joint connecting the other end of the rod means with said trimming means, a push-pull rod operatively connected at one end with the tab and pivotally connected at its other end with the lever in spaced relation to saidpivot, control means operable by the pilot, a second lever pivotally mounted on the control surface for movement about said given axis and connected to said control means to be operated thereby, a preloaded two-way acting spring unit operating between the control surface and said second lever to cause coordinated and relative angular movements of the control surface and said second leverin response to loads acting. thereupon, and transmission meansinterconnecting said second and first levers to transfer movements from said second lever to said first lever.

3. In-an aircraft, a control surface pivotally connected at its forward edge to the aircraft for movement about a given axis, a tab hinged to the trailing edge of the control surface, a steering arm pivotally supported at one end by the control surface at an axis spacedat one side of said given axis, a two-armed lever pivotally supported by the other end of the steering arm at an axis spaced at the other side of said given 1 axis, trim adjustment means for trimming the position ofthe tab relatively to the control surface, said trim adjustment means being mounted stationary on the aircraft, a rod universally pivotally connected at one end with the trim adjustment means and pivotally mounted at its other end with one arm of the lever at an axis spaced at said one side of said given axis, a pushpull rod pivotally connecting the other arm of the lever with the tab, control means operable by the pilot, a second lever pivotally mounted on the control surface for movement about said given axis and connected to said control means to be face and said second lever to cause coordinated and relative angular movements of the control surface and said second lever in response to loads acting thereupon, and transmission means interconnecting said second and first levers to transfer movements from said second lever to said first lever.

2. In an aircraft, a control surface pivotally connected at its forward edge to the aircraft for movement about a given axis, a tab hinged to the trailing edge of the control surface, a lever, a steering means supported by the control surface and extending in a plane normal to said given axis, a pivotal connection between the lever and the steering means, said lever beingsupported by the steering means for bodilymovement of the lever in said plane and turning movement of the operated thereby, a pre-loaded two-way acting spring unit connected between the control surface and said second lever to cause coordinated and relative angular movements of the control surface and said second lever in response to loads acting thereupon, transmission means comprising a torsion tube rotatably mounted on stationary parts of the aircraft, and rods pivotally connecting the torsion tube with said other end of the steering arm and with said second lever respectively to transfer angular movements from said second lever to said first lever.

TORD' NILS GOSTA LIDMAIM. 1 V NILS FOLKELENNART BENGTSSON.

References Citedin the file of this patent UNITED STATES PATENTS Great Britain Dec. 2', 1947 OTHER REFERENCES Aircraft Engineering October 1947, p. 316, British Magazine, vol. XIX, No. 224. Copy in Div. 22. Y 

